I don't really know the whole procedure. My friend told me that in for example a loop there is a difference in pressure and the whole covering is working. I can't really say how it works.
This airfoil works best with the tip covered in balsa and the rest only by the covering. I will later write and make some photos of how to draw this airfoil.
P.S. I can only write something in the quick reply. Why can't I also submit a "normal" reply and start new threads?